package com.harboursoftware.xstorage.util;

import java.lang.ref.SoftReference;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.TimeZone;

/**
 * A utility class for parsing and formatting HTTP dates as used in cookies and other headers. This class handles dates
 * as defined by RFC 2616 section 3.3.1 as well as some other common non-standard formats.
 * 
 * 
 * @since 0.1
 * @author Apache HttpClient
 */
public final class DateUtils {

    /**
     * Date format pattern used to parse HTTP date headers in RFC 1123 format.
     */
    public static final String PATTERN_RFC1123 = "EEE, dd MMM yyyy HH:mm:ss zzz";

    /**
     * Date format pattern used to parse HTTP date headers in RFC 1036 format.
     */
    public static final String PATTERN_RFC1036 = "EEEE, dd-MMM-yy HH:mm:ss zzz";

    /**
     * Date format pattern used to parse HTTP date headers in ANSI C <code>asctime()</code> format.
     */
    public static final String PATTERN_ASCTIME = "EEE MMM d HH:mm:ss yyyy";
    
    public static final String PATTERN_ISO8601 = "yyyy-MM-dd'T'kk:mm:ss.SSS'Z'";

    private static final String[] DEFAULT_PATTERNS = new String[] { PATTERN_RFC1036, PATTERN_RFC1123, PATTERN_ASCTIME };

    private static final Date DEFAULT_TWO_DIGIT_YEAR_START;

    public static final TimeZone GMT = TimeZone.getTimeZone("GMT");

    static {
        Calendar calendar = Calendar.getInstance();
        calendar.setTimeZone(GMT);
        calendar.set(2000, Calendar.JANUARY, 1, 0, 0, 0);
        calendar.set(Calendar.MILLISECOND, 0);
        DEFAULT_TWO_DIGIT_YEAR_START = calendar.getTime();
    }

    /**
     * Parses a date value. The formats used for parsing the date value are retrieved from the default http params.
     * 
     * @param dateValue
     *            the date value to parse
     * 
     * @return the parsed date
     * 
     * @throws DateParseException
     *             if the value could not be parsed using any of the supported date formats
     */
    public static Date parseDate(String dateValue) throws DateParseException {
        return parseDate(dateValue, null, null);
    }
    
    /**
     * Parses the date value using the given date format.
     * 
     * @param dateValue
     *            the date value to parse
     * @param dateFormat
     *            the date format to use
     * 
     * @return the parsed date
     * 
     * @throws DateParseException
     *             if none of the dataFormats could parse the dateValue
     */
    public static Date parseDate(final String dateValue, String dateFormat) throws DateParseException {
        return parseDate(dateValue, new String[]{dateFormat});
    }

    /**
     * Parses the date value using the given date formats.
     * 
     * @param dateValue
     *            the date value to parse
     * @param dateFormats
     *            the date formats to use
     * 
     * @return the parsed date
     * 
     * @throws DateParseException
     *             if none of the dataFormats could parse the dateValue
     */
    public static Date parseDate(final String dateValue, String[] dateFormats) throws DateParseException {
        return parseDate(dateValue, dateFormats, null);
    }

    /**
     * Parses the date value using the given date formats.
     * 
     * @param dateValue
     *            the date value to parse
     * @param dateFormats
     *            the date formats to use
     * @param startDate
     *            During parsing, two digit years will be placed in the range <code>startDate</code> to
     *            <code>startDate + 100 years</code>. This value may be <code>null</code>. When <code>null</code> is
     *            given as a parameter, year <code>2000</code> will be used.
     * 
     * @return the parsed date
     * 
     * @throws DateParseException
     *             if none of the dataFormats could parse the dateValue
     */
    public static Date parseDate(String dateValue, String[] dateFormats, Date startDate) throws DateParseException {

        if (dateValue == null) {
            throw new IllegalArgumentException("dateValue is null");
        }
        if (dateFormats == null) {
            dateFormats = DEFAULT_PATTERNS;
        }
        if (startDate == null) {
            startDate = DEFAULT_TWO_DIGIT_YEAR_START;
        }
        // trim single quotes around date if present
        // see issue #5279
        if (dateValue.length() > 1 && dateValue.startsWith("'") && dateValue.endsWith("'")) {
            dateValue = dateValue.substring(1, dateValue.length() - 1);
        }

        for (String dateFormat : dateFormats) {
            SimpleDateFormat dateParser = DateFormatHolder.formatFor(dateFormat);
            dateParser.set2DigitYearStart(startDate);

            try {
                return dateParser.parse(dateValue);
            } catch (ParseException pe) {
                // ignore this exception, we will try the next format
            }
        }

        // we were unable to parse the date
        throw new DateParseException("Unable to parse the date " + dateValue);
    }

    /**
     * Formats the given date according to the RFC 1123 pattern.
     * 
     * @param date
     *            The date to format.
     * @return An RFC 1123 formatted date string.
     * 
     * @see #PATTERN_RFC1123
     */
    public static String formatDate(Date date) {
        return formatDate(date, PATTERN_RFC1123);
    }

    /**
     * Formats the given date according to the specified pattern. The pattern must conform to that used by the
     * {@link SimpleDateFormat simple date format} class.
     * 
     * @param date
     *            The date to format.
     * @param pattern
     *            The pattern to use for formatting the date.
     * @return A formatted date string.
     * 
     * @throws IllegalArgumentException
     *             If the given date pattern is invalid.
     * 
     * @see SimpleDateFormat
     */
    public static String formatDate(Date date, String pattern) {
        if (date == null)
            throw new IllegalArgumentException("date is null");
        if (pattern == null)
            throw new IllegalArgumentException("pattern is null");

        SimpleDateFormat formatter = DateFormatHolder.formatFor(pattern);
        return formatter.format(date);
    }

    /** This class should not be instantiated. */
    private DateUtils() {
    }

    /**
     * A factory for {@link SimpleDateFormat}s. The instances are stored in a threadlocal way because SimpleDateFormat
     * is not threadsafe as noted in {@link SimpleDateFormat its javadoc}.
     * 
     */
    final static class DateFormatHolder {

        private static final ThreadLocal<SoftReference<Map<String, SimpleDateFormat>>> THREADLOCAL_FORMATS =
            new ThreadLocal<SoftReference<Map<String, SimpleDateFormat>>>() {

                @Override
                protected SoftReference<Map<String, SimpleDateFormat>> initialValue() {
                    return new SoftReference<Map<String, SimpleDateFormat>>(new HashMap<String, SimpleDateFormat>());
                }

            };

        /**
         * creates a {@link SimpleDateFormat} for the requested format string.
         * 
         * @param pattern
         *            a non-<code>null</code> format String according to {@link SimpleDateFormat}. The format is not
         *            checked against <code>null</code> since all paths go through {@link DateUtils}.
         * @return the requested format. This simple dateformat should not be used to
         *         {@link SimpleDateFormat#applyPattern(String) apply} to a different pattern.
         */
        public static SimpleDateFormat formatFor(String pattern) {
            SoftReference<Map<String, SimpleDateFormat>> ref = THREADLOCAL_FORMATS.get();
            Map<String, SimpleDateFormat> formats = ref.get();
            if (formats == null) {
                formats = new HashMap<String, SimpleDateFormat>();
                THREADLOCAL_FORMATS.set(new SoftReference<Map<String, SimpleDateFormat>>(formats));
            }

            SimpleDateFormat format = formats.get(pattern);
            if (format == null) {
                format = new SimpleDateFormat(pattern, Locale.US);
                format.setTimeZone(TimeZone.getTimeZone("GMT"));
                formats.put(pattern, format);
            }

            return format;
        }

    }

}
